You are arguing against a straw-man. I wasn't talking about the standard. The behaviour is, as you say, implementation defined. So, Microsoft are perfectly free

You are arguing against a straw-man. I wasn't talking about the standard. The behaviour is, as you say, implementation defined. So, Microsoft are perfectly free to implement volatile access from multiple threads as re-formatting the hard-drive or whatever. What I did say is that Microsoft have chosen to implement volatile access in a way that is incompatible with other compilers. Their choice to put the barriers in for you is certainly well-intentioned, but really just complicates matters.